Increased emphasis has been placed on designing aircraft for STOL operation from, for example, austere airfields; however, current powered-lift STOL designs fail to optimize the aircraft configuration for both STOL and cruise performance. Because large pitching moments and engine-out yawing and rolling moments are associated with known powered-lift STOL aircraft, the conventional aircraft, configured for STOL performance, requires large control surfaces. These large control surfaces result in an increase in overall weight as well as in a drag penalty at cruise speeds. Furthermore, even with the use of large control surfaces, the airspeed needed for minimum control is relatively high compared to that which is theoretically obtainable.
Since the above-noted lower potential takeoff speed is not utilized by known STOL aircraft, heretofore, increased thrust has been employed to accelerate the aircraft to the required speed necessary to meet takeoff requirements. As a result, the engine of a STOL aircraft is often over-designed for cruise performance which results in a higher rate of fuel consumption than an engine specifically adapted for cruise operation.
Additionally, STOL aircraft takeoff speeds, and consequently distances have been controlled, to a large extent, by the inability to rotate at low speeds and by pitch limitations imposed by tail strike geometry. Thus, known powered-lift STOL designs impose drag and weight penalties on an aircraft during cruise operation in connection with a design which is useful for only a short period of time during the operation of the aircraft.
In an attempt to overcome the above-noted problems, alternative, non-aerodynamic design approaches have been proposed. One such solution is the use of an in situ "ski ramp" device positioned, during takeoff, on a runway for use with an aircraft essentially designed for cruise operation. The ramp deflects some ground run momentum upwards before the aircraft reaches flight speed, the resulting trajectory permitting continued velocity increase up to flight speed without additional ground run.
Another approach being investigated is the use of a jump strut landing gear device utilizing a pneumatically charged chamber which is mechanically latched in a compressed position under a high load until the moment of release. By sequentially releasing the nose and main landing gear latches, the compressed charge extends the landing gear strut to achieve the desired "ski jump" effect.
Traditionally, the purpose of aircraft landing gear has been to absorb energy during touchdown, facilitate ground maneuver, assist in braking the aircraft during runway operation, provide adequate taildown angle for takeoff, and assure the stable support of the aircraft while on the ground. The typical, known landing gear comprises shock absorbers, wheels, tires, brakes, as well as necessary linkages and structures.
Thus, in the past, aircraft landing gear has been designed primarily for absorption of landing impact forces with little or no consideration for STOL operation on austere landing fields having rough ground surfaces. As noted above, significant operational benefits result by providing a stored energy capability within the landing gear. However, the latched-pneumatic charged system presents some energy management problems as well as wear and sequencing considerations due to the requirement that unlatching occurs at high loads. Additionally, operating a charged system for extended periods of time results in reliability and risk concerns.